<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>WebGL - 3D Camera Look At Heads</title>
    <link type="text/css" href="../resources/webgl-tutorials.css" rel="stylesheet" />
</head>

<body>
    <div id="info">
        <div class="description">
            Drag slider to move camera.
        </div>
        <a href="https://webglfundamentals.org/webgl/lessons/zh_cn/webgl-3d-camera.html" target="_blank">WebGL 三维相机</a>
    </div>
    <canvas id="canvas"></canvas>
    <div id="uiContainer">
        <div id="ui">
            <div id="targetAngle"></div>
            <div id="targetHeight"></div>
        </div>
    </div>
</body>
<!-- vertex shader -->
<script id="3d-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec4 a_color;

uniform mat4 u_matrix;

varying vec4 v_color;

void main() {
  // Multiply the position by the matrix.
  gl_Position = u_matrix * a_position;

  // Pass the color to the fragment shader.
  v_color = a_color;
}
</script>
<!-- fragment shader -->
<script id="3d-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

// Passed in from the vertex shader.
varying vec4 v_color;

void main() {
   gl_FragColor = v_color;
}
</script>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See http://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and http://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="../resources/webgl-utils.js"></script>
<script src="../resources/webgl-lessons-ui.js"></script>
<script src="../resources/headdata.js"></script>
<script>
    "use strict";

    function main() {
        // Get A WebGL context
        /** @type {HTMLCanvasElement} */
        var canvas = document.getElementById("canvas");
        var gl = canvas.getContext("webgl");
        if (!gl) {
            return;
        }

        // setup GLSL program
        var program = webglUtils.createProgramFromScripts(gl, ["3d-vertex-shader", "3d-fragment-shader"]);
        gl.useProgram(program);

        // look up where the vertex data needs to go.
        var positionLocation = gl.getAttribLocation(program, "a_position");
        var colorLocation = gl.getAttribLocation(program, "a_color");

        // lookup uniforms
        var matrixLocation = gl.getUniformLocation(program, "u_matrix");

        // Create a buffer to put positions in
        var positionBuffer = gl.createBuffer();
        // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
        gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
        // Put geometry data into buffer
        var numElements = setGeometry(gl);

        // Create a buffer to put colors in
        var colorBuffer = gl.createBuffer();
        // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = colorBuffer)
        gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
        // Put geometry data into buffer
        setColors(gl);

        function radToDeg(r) {
            return r * 180 / Math.PI;
        }

        function degToRad(d) {
            return d * Math.PI / 180;
        }

        var target = [0, 200, 300];
        var targetAngleRadians = 0;
        var targetRadius = 300;
        var fieldOfViewRadians = degToRad(60);

        drawScene();

        // Setup a ui.
        webglLessonsUI.setupSlider("#targetAngle", { value: radToDeg(targetAngleRadians), slide: updateTargetAngle, min: -360, max: 360 });
        webglLessonsUI.setupSlider("#targetHeight", { value: target[1], slide: updateTargetHeight, min: 50, max: 300 });

        function updateTargetAngle(event, ui) {
            targetAngleRadians = degToRad(ui.value);
            target[0] = Math.sin(targetAngleRadians) * targetRadius;
            target[2] = Math.cos(targetAngleRadians) * targetRadius;
            drawScene();
        }

        function updateTargetHeight(event, ui) {
            target[1] = ui.value;
            drawScene();
        }


        // Draw the scene.
        function drawScene() {
            var numFs = 5;
            var radius = 600;

            webglUtils.resizeCanvasToDisplaySize(gl.canvas);

            // Tell WebGL how to convert from clip space to pixels
            gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

            // Clear the canvas AND the depth buffer.
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

            // Turn on culling. By default backfacing triangles
            // will be culled.
            gl.enable(gl.CULL_FACE);

            // Enable the depth buffer
            gl.enable(gl.DEPTH_TEST);

            // Tell it to use our program (pair of shaders)
            gl.useProgram(program);

            // Turn on the position attribute
            gl.enableVertexAttribArray(positionLocation);

            // Bind the position buffer.
            gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

            // Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
            var size = 3;          // 3 components per iteration
            var type = gl.FLOAT;   // the data is 32bit floats
            var normalize = false; // don't normalize the data
            var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
            var offset = 0;        // start at the beginning of the buffer
            gl.vertexAttribPointer(
                positionLocation, size, type, normalize, stride, offset);

            // Turn on the color attribute
            gl.enableVertexAttribArray(colorLocation);

            // Bind the color buffer.
            gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);

            // Tell the attribute how to get data out of colorBuffer (ARRAY_BUFFER)
            var size = 3;                 // 3 components per iteration
            var type = gl.UNSIGNED_BYTE;  // the data is 8bit unsigned values
            var normalize = true;         // normalize the data (convert from 0-255 to 0-1)
            var stride = 0;               // 0 = move forward size * sizeof(type) each iteration to get the next position
            var offset = 0;               // start at the beginning of the buffer
            gl.vertexAttribPointer(
                colorLocation, size, type, normalize, stride, offset);

            // Compute the projection matrix
            var aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
            var zNear = 1;
            var zFar = 3000;
            var projectionMatrix = m4.perspective(fieldOfViewRadians, aspect, zNear, zFar);

            var cameraTarget = [0, -100, 0];
            var cameraPosition = [500, 300, 500];
            var up = [0, 1, 0];

            // Compute the camera's matrix using look at.
            var cameraMatrix = m4.lookAt(cameraPosition, cameraTarget, up);

            // Make a view matrix from the camera matrix.
            var viewMatrix = m4.inverse(cameraMatrix);

            // create a viewProjection matrix. This will both apply perspective
            // AND move the world so that the camera is effectively the origin
            var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);

            // Draw heads in a grid
            var deep = 5;
            var across = 5;
            for (var zz = 0; zz < deep; ++zz) {
                var v = zz / (deep - 1);
                var z = (v - .5) * deep * 150;
                for (var xx = 0; xx < across; ++xx) {
                    var u = xx / (across - 1);
                    var x = (u - .5) * across * 150;
                    var matrix = m4.lookAt([x, 0, z], target, up);
                    drawHead(matrix, viewProjectionMatrix, matrixLocation, numElements);
                }
            }

            drawHead(m4.translation(target[0], target[1], target[2]), viewProjectionMatrix, matrixLocation, numElements);
        }

        function drawHead(matrix, viewProjectionMatrix, matrixLocation, numElements) {
            // multiply that with the viewProjecitonMatrix
            matrix = m4.multiply(viewProjectionMatrix, matrix);

            // Set the matrix.
            gl.uniformMatrix4fv(matrixLocation, false, matrix);

            // Draw the geometry.
            var primitiveType = gl.TRIANGLES;
            var offset = 0;
            gl.drawArrays(gl.TRIANGLES, 0, numElements);
        }
    }

    function subtractVectors(a, b) {
        return [a[0] - b[0], a[1] - b[1], a[2] - b[2]];
    }

    function normalize(v) {
        var length = Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
        // make sure we don't divide by 0.
        if (length > 0.00001) {
            return [v[0] / length, v[1] / length, v[2] / length];
        } else {
            return [0, 0, 0];
        }
    }

    function cross(a, b) {
        return [a[1] * b[2] - a[2] * b[1],
        a[2] * b[0] - a[0] * b[2],
        a[0] * b[1] - a[1] * b[0]];
    }



    var m4 = {

        lookAt: function (cameraPosition, target, up) {
            var zAxis = normalize(
                subtractVectors(cameraPosition, target));
            var xAxis = normalize(cross(up, zAxis));
            var yAxis = normalize(cross(zAxis, xAxis));

            return [
                xAxis[0], xAxis[1], xAxis[2], 0,
                yAxis[0], yAxis[1], yAxis[2], 0,
                zAxis[0], zAxis[1], zAxis[2], 0,
                cameraPosition[0],
                cameraPosition[1],
                cameraPosition[2],
                1,
            ];
        },

        perspective: function (fieldOfViewInRadians, aspect, near, far) {
            var f = Math.tan(Math.PI * 0.5 - 0.5 * fieldOfViewInRadians);
            var rangeInv = 1.0 / (near - far);

            return [
                f / aspect, 0, 0, 0,
                0, f, 0, 0,
                0, 0, (near + far) * rangeInv, -1,
                0, 0, near * far * rangeInv * 2, 0
            ];
        },

        projection: function (width, height, depth) {
            // Note: This matrix flips the Y axis so 0 is at the top.
            return [
                2 / width, 0, 0, 0,
                0, -2 / height, 0, 0,
                0, 0, 2 / depth, 0,
                -1, 1, 0, 1,
            ];
        },

        multiply: function (a, b) {
            var a00 = a[0 * 4 + 0];
            var a01 = a[0 * 4 + 1];
            var a02 = a[0 * 4 + 2];
            var a03 = a[0 * 4 + 3];
            var a10 = a[1 * 4 + 0];
            var a11 = a[1 * 4 + 1];
            var a12 = a[1 * 4 + 2];
            var a13 = a[1 * 4 + 3];
            var a20 = a[2 * 4 + 0];
            var a21 = a[2 * 4 + 1];
            var a22 = a[2 * 4 + 2];
            var a23 = a[2 * 4 + 3];
            var a30 = a[3 * 4 + 0];
            var a31 = a[3 * 4 + 1];
            var a32 = a[3 * 4 + 2];
            var a33 = a[3 * 4 + 3];
            var b00 = b[0 * 4 + 0];
            var b01 = b[0 * 4 + 1];
            var b02 = b[0 * 4 + 2];
            var b03 = b[0 * 4 + 3];
            var b10 = b[1 * 4 + 0];
            var b11 = b[1 * 4 + 1];
            var b12 = b[1 * 4 + 2];
            var b13 = b[1 * 4 + 3];
            var b20 = b[2 * 4 + 0];
            var b21 = b[2 * 4 + 1];
            var b22 = b[2 * 4 + 2];
            var b23 = b[2 * 4 + 3];
            var b30 = b[3 * 4 + 0];
            var b31 = b[3 * 4 + 1];
            var b32 = b[3 * 4 + 2];
            var b33 = b[3 * 4 + 3];
            return [
                b00 * a00 + b01 * a10 + b02 * a20 + b03 * a30,
                b00 * a01 + b01 * a11 + b02 * a21 + b03 * a31,
                b00 * a02 + b01 * a12 + b02 * a22 + b03 * a32,
                b00 * a03 + b01 * a13 + b02 * a23 + b03 * a33,
                b10 * a00 + b11 * a10 + b12 * a20 + b13 * a30,
                b10 * a01 + b11 * a11 + b12 * a21 + b13 * a31,
                b10 * a02 + b11 * a12 + b12 * a22 + b13 * a32,
                b10 * a03 + b11 * a13 + b12 * a23 + b13 * a33,
                b20 * a00 + b21 * a10 + b22 * a20 + b23 * a30,
                b20 * a01 + b21 * a11 + b22 * a21 + b23 * a31,
                b20 * a02 + b21 * a12 + b22 * a22 + b23 * a32,
                b20 * a03 + b21 * a13 + b22 * a23 + b23 * a33,
                b30 * a00 + b31 * a10 + b32 * a20 + b33 * a30,
                b30 * a01 + b31 * a11 + b32 * a21 + b33 * a31,
                b30 * a02 + b31 * a12 + b32 * a22 + b33 * a32,
                b30 * a03 + b31 * a13 + b32 * a23 + b33 * a33,
            ];
        },

        translation: function (tx, ty, tz) {
            return [
                1, 0, 0, 0,
                0, 1, 0, 0,
                0, 0, 1, 0,
                tx, ty, tz, 1,
            ];
        },

        xRotation: function (angleInRadians) {
            var c = Math.cos(angleInRadians);
            var s = Math.sin(angleInRadians);

            return [
                1, 0, 0, 0,
                0, c, s, 0,
                0, -s, c, 0,
                0, 0, 0, 1,
            ];
        },

        yRotation: function (angleInRadians) {
            var c = Math.cos(angleInRadians);
            var s = Math.sin(angleInRadians);

            return [
                c, 0, -s, 0,
                0, 1, 0, 0,
                s, 0, c, 0,
                0, 0, 0, 1,
            ];
        },

        zRotation: function (angleInRadians) {
            var c = Math.cos(angleInRadians);
            var s = Math.sin(angleInRadians);

            return [
                c, s, 0, 0,
                -s, c, 0, 0,
                0, 0, 1, 0,
                0, 0, 0, 1,
            ];
        },

        scaling: function (sx, sy, sz) {
            return [
                sx, 0, 0, 0,
                0, sy, 0, 0,
                0, 0, sz, 0,
                0, 0, 0, 1,
            ];
        },

        translate: function (m, tx, ty, tz) {
            return m4.multiply(m, m4.translation(tx, ty, tz));
        },

        xRotate: function (m, angleInRadians) {
            return m4.multiply(m, m4.xRotation(angleInRadians));
        },

        yRotate: function (m, angleInRadians) {
            return m4.multiply(m, m4.yRotation(angleInRadians));
        },

        zRotate: function (m, angleInRadians) {
            return m4.multiply(m, m4.zRotation(angleInRadians));
        },

        scale: function (m, sx, sy, sz) {
            return m4.multiply(m, m4.scaling(sx, sy, sz));
        },

        inverse: function (m) {
            var m00 = m[0 * 4 + 0];
            var m01 = m[0 * 4 + 1];
            var m02 = m[0 * 4 + 2];
            var m03 = m[0 * 4 + 3];
            var m10 = m[1 * 4 + 0];
            var m11 = m[1 * 4 + 1];
            var m12 = m[1 * 4 + 2];
            var m13 = m[1 * 4 + 3];
            var m20 = m[2 * 4 + 0];
            var m21 = m[2 * 4 + 1];
            var m22 = m[2 * 4 + 2];
            var m23 = m[2 * 4 + 3];
            var m30 = m[3 * 4 + 0];
            var m31 = m[3 * 4 + 1];
            var m32 = m[3 * 4 + 2];
            var m33 = m[3 * 4 + 3];
            var tmp_0 = m22 * m33;
            var tmp_1 = m32 * m23;
            var tmp_2 = m12 * m33;
            var tmp_3 = m32 * m13;
            var tmp_4 = m12 * m23;
            var tmp_5 = m22 * m13;
            var tmp_6 = m02 * m33;
            var tmp_7 = m32 * m03;
            var tmp_8 = m02 * m23;
            var tmp_9 = m22 * m03;
            var tmp_10 = m02 * m13;
            var tmp_11 = m12 * m03;
            var tmp_12 = m20 * m31;
            var tmp_13 = m30 * m21;
            var tmp_14 = m10 * m31;
            var tmp_15 = m30 * m11;
            var tmp_16 = m10 * m21;
            var tmp_17 = m20 * m11;
            var tmp_18 = m00 * m31;
            var tmp_19 = m30 * m01;
            var tmp_20 = m00 * m21;
            var tmp_21 = m20 * m01;
            var tmp_22 = m00 * m11;
            var tmp_23 = m10 * m01;

            var t0 = (tmp_0 * m11 + tmp_3 * m21 + tmp_4 * m31) -
                (tmp_1 * m11 + tmp_2 * m21 + tmp_5 * m31);
            var t1 = (tmp_1 * m01 + tmp_6 * m21 + tmp_9 * m31) -
                (tmp_0 * m01 + tmp_7 * m21 + tmp_8 * m31);
            var t2 = (tmp_2 * m01 + tmp_7 * m11 + tmp_10 * m31) -
                (tmp_3 * m01 + tmp_6 * m11 + tmp_11 * m31);
            var t3 = (tmp_5 * m01 + tmp_8 * m11 + tmp_11 * m21) -
                (tmp_4 * m01 + tmp_9 * m11 + tmp_10 * m21);

            var d = 1.0 / (m00 * t0 + m10 * t1 + m20 * t2 + m30 * t3);

            return [
                d * t0,
                d * t1,
                d * t2,
                d * t3,
                d * ((tmp_1 * m10 + tmp_2 * m20 + tmp_5 * m30) -
                    (tmp_0 * m10 + tmp_3 * m20 + tmp_4 * m30)),
                d * ((tmp_0 * m00 + tmp_7 * m20 + tmp_8 * m30) -
                    (tmp_1 * m00 + tmp_6 * m20 + tmp_9 * m30)),
                d * ((tmp_3 * m00 + tmp_6 * m10 + tmp_11 * m30) -
                    (tmp_2 * m00 + tmp_7 * m10 + tmp_10 * m30)),
                d * ((tmp_4 * m00 + tmp_9 * m10 + tmp_10 * m20) -
                    (tmp_5 * m00 + tmp_8 * m10 + tmp_11 * m20)),
                d * ((tmp_12 * m13 + tmp_15 * m23 + tmp_16 * m33) -
                    (tmp_13 * m13 + tmp_14 * m23 + tmp_17 * m33)),
                d * ((tmp_13 * m03 + tmp_18 * m23 + tmp_21 * m33) -
                    (tmp_12 * m03 + tmp_19 * m23 + tmp_20 * m33)),
                d * ((tmp_14 * m03 + tmp_19 * m13 + tmp_22 * m33) -
                    (tmp_15 * m03 + tmp_18 * m13 + tmp_23 * m33)),
                d * ((tmp_17 * m03 + tmp_20 * m13 + tmp_23 * m23) -
                    (tmp_16 * m03 + tmp_21 * m13 + tmp_22 * m23)),
                d * ((tmp_14 * m22 + tmp_17 * m32 + tmp_13 * m12) -
                    (tmp_16 * m32 + tmp_12 * m12 + tmp_15 * m22)),
                d * ((tmp_20 * m32 + tmp_12 * m02 + tmp_19 * m22) -
                    (tmp_18 * m22 + tmp_21 * m32 + tmp_13 * m02)),
                d * ((tmp_18 * m12 + tmp_23 * m32 + tmp_15 * m02) -
                    (tmp_22 * m32 + tmp_14 * m02 + tmp_19 * m12)),
                d * ((tmp_22 * m22 + tmp_16 * m02 + tmp_21 * m12) -
                    (tmp_20 * m12 + tmp_23 * m22 + tmp_17 * m02))
            ];
        },

        vectorMultiply: function (v, m) {
            var dst = [];
            for (var i = 0; i < 4; ++i) {
                dst[i] = 0.0;
                for (var j = 0; j < 4; ++j) {
                    dst[i] += v[j] * m[j * 4 + i];
                }
            }
            return dst;
        },

    };


    // Fill the buffer with the values that define a letter 'F'.
    function setGeometry(gl) {
        var positions = new Float32Array(HeadData.positions);
        var matrix = m4.multiply(m4.scaling(6, 6, 6), m4.yRotation(Math.PI));
        for (var ii = 0; ii < positions.length; ii += 3) {
            var vector = m4.vectorMultiply([positions[ii + 0], positions[ii + 1], positions[ii + 2], 1], matrix);
            positions[ii + 0] = vector[0];
            positions[ii + 1] = vector[1];
            positions[ii + 2] = vector[2];
        }

        gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
        return positions.length / 3;
    }

    // Fill the buffer with colors for the 'F'.
    function setColors(gl, numElements) {
        var normals = HeadData.normals;
        var colors = new Uint8Array(normals.length);
        var offset = 0;
        for (var ii = 0; ii < colors.length; ii += 3) {
            for (var jj = 0; jj < 3; ++jj) {
                colors[offset] = (normals[offset] * 0.5 + 0.5) * 255;
                ++offset;
            }
        }
        gl.bufferData(
            gl.ARRAY_BUFFER, colors, gl.STATIC_DRAW);
    }

    main();
</script>

</html>